1. Field of the Invention
The present invention relates to a gear decision system for an automatic transmission (speed change gear) which decides whether or not the automatic transmission establishes an in-gear state (linking state) and which is available for control of an engine of a motor vehicle, and more particularly to an automatic transmission gear decision system which surely prevents erroneous decisions to improve reliability for various control.
2. Description of the Prior Art
As a rule, in a motor vehicle equipped with an automatic transmission, its starter is designed to operate (come into the on-condition) when its shift lever takes the N (neutral) position or the P (parking) position and further its automatic transmission does not establish an in-gear state (out of gear), that is, when the engine is in no-load condition. In addition, the decision on the in-gear state of the automatic transmission depends upon various operating conditions, while the decision result is reflected in various control. For this reason, an accurate decision on the in-gear state is necessary. For the decision on the in-gear state, an engine control system of such a motor vehicle includes a gear decision unit responsive to, for example, a no-load switch.
FIG. 6 illustrates an arrangement of an engine control system including a prior art gear decision unit for an automatic transmission. In the illustration, air A to be sucked into an engine 1 is taken in through an air cleaner 2 from the atmosphere and then passes through an air quantity sensor 3 for sensing an intake air quantity Qa, a duct 4 making up an intake pipe and a throttle valve 5 for adjusting the intake air quantity Qa in sequence, and thereafter is led into cylinders 6.
The output signal of the air quantity sensor 3 representative of the intake air quantity Qa is inputted into a control unit (which will be referred hereinafter to as an ECU) 10. The ECU 10, comprising a microcomputer, serves as a variety of control means, automatic transmission gear decision means and so on as will be described later. A throttle sensor 7 is provided in connection with the throttle valve 5 so as to sense an opening degree .theta. of the throttle valve 5, and issues a signal indicative of the throttle opening degree .theta. and supplies it to the ECU 10. Further, a crank angle sensor 8 is attached onto a crank shaft K of the engine 1 to sense given crank angles in response to the rotation of the engine 1, and produces a reference signal CA being a pulse generated at every reference angle and delivers it to the ECU 10.
A starter 9 comprising a motor provided on the engine 1 is connected through a starter switch 11 associated with a keyswitch (not shown) to a battery B so that it is driven by the operation of the starter switch 11 to start the engine 1. An injector 12, being controlled in accordance with a fuel injection signal CF from the ECU 10, is located at an upstream side of each cylinder 6 to mix the air A with fuel F pressurized and delivered from a fuel tank (not shown) by means of a pump and to supply the mixture into each cylinder 6. Further, an ignition coil 13, being controlled in accordance with an ignition signal CP from the ECU 10, generates a high voltage E to operate an ignition plug 14 placed in each cylinder 6. The exhaust gas, produced by the combustion of the mixture within each cylinder 6 of the engine 1 due to the discharge of the ignition plug 14, is released through an exhaust pipe and a catalyst (not shown) toward the atmosphere.
An automatic transmission 18, being controlled in accordance with a speed change signal CG from the ECU 10, accomplishes an aiming gear shift (gear position) using a solenoid 15 operable by the speed change signal CG therefrom. In connection with the automatic transmission 18, there are provided a vehicle speed sensor 16 attached onto the output shaft of the automatic transmission 18 to sense the speed V of the motor vehicle and a turbine speed sensor 17 for sensing the speed Rt of a turbine located inside the automatic transmission 18. The vehicle speed V and turbine speed Rt from these sensors 16, 17 are inputted as speed change information to the ECU 10. Furthermore, in conjunction with a shift lever (not shown) manipulated by the vehicle driver, there is placed a no-load switch 19 which is made to come into the on-state when the shift lever takes the N position or the P position. Under the conditions that the shift lever takes the N or P position and the no-load state is detected, the no-load switch 19 supplies the ECU 10 with a no-load signal NL, for example, taking a low-level state.
FIG. 7 is a block diagram showing a portion of a functional arrangement of the ECU 10. In this instance, a signal is not inputted from the starter switch 11 to the ECU 10 from the viewpoint of cost reduction. The ECU 10 includes a start decision means 24 for outputting a start signal St in response to the detection of the on-state (the start-up) of the starter 9 and a gear decision means 25 for checking, on the basis of the no-load signal NL and the start signal St, whether or not the automatic transmission is in gear so as to transmit a power. The start decision means 24 outputs a decision result, i.e., the start signal St indicative of the start-up on the basis of information other than the starter switch 11 information, for example, when the engine speed Re corresponding to the turbine speed Rt is below a given set value Reo (the engine speed at cranking, approximately 300 rpm). In general, in an automatic transmission 18 mounted motor vehicle, the cranking state occurs only when the automatic transmission 18 is not in the power transmitting condition. Accordingly, the starter 9 is designed to get into the on-condition only when the gear decision means 25 decides that the automatic transmission 18 is not in the power transmitting condition.
FIG. 8 is an illustration of an arrangement of a control function of the starter 9 such as disclosed in Japanese Published Unexamined Patent Application No. 3-109137, where a relay L is used as a driving circuit for the starter 9. The relay L, controlled with the ECU 10, is composed of a relay coil LC energized by a relay signal CL from the ECU 10 and a relay switch LS closed in response to the energization of the relay coil LC. The relay switch LS is coupled in series to the starter 9. In this case, not only the no-load switch 19 but also a brake switch BS are in connecting relation to the ECU 10, and the brake switch BS supplies a brake signal BK to the ECU 10 in a state where the vehicle driver presses the brake pedal. The ECU 10 turns on the relay L to operate the starter 9 only when the no-load switch 19 is in the on-state and the brake pedal is in a pressed state (the brake switch BS is in the on-state).
Furthermore, it is also possible that as shown in FIG. 9 the function of the relay L is achieved with a hardware arrangement and the starter 9 is made so as not to rotate when the automatic transmission 18 takes the in-gear state. In FIG. 9, the no-load switch 19 is interposed between the starter 9 and the starter switch 11 and the no-load voltage EN at the junction (node) between the no-load switch 19 and the starter switch 11 is inputted to the ECU 10. More specifically, the no-load voltage EN is pulled up to the power supply voltage, before being applied to an input terminal of a CPU (central processing unit) within the ECU 10.
Secondly, a description will be made hereinbelow with reference to FIGS. 6 to 9 in terms of an operation of the prior automatic transmission gear decision system. As a rule, in the case that the engine 1 starts in a state with having been in the stopped condition, the starter switch 11 is turned on through the manipulation of the keyswitch. In this case, as shown in FIG. 9, a current flows into the starter 9 only when the shift lever takes the N or P position (the no-load switch 19 is in the operated state), that is, only at the time of the no-load condition, so that the starter 9 can rotate to start the engine 1. Further, if at this time the start decision means 24 (see FIG. 7) outputs the start signal St indicative of the fact that the engine 1 is on the start-up, the gear decision means 25 decides that the automatic transmission 18 takes the out-of-gear state, irrespective of the state of the no-load switch 19 (the presence or absence of the no-load signal NL).
Now, let it be assumed that the vehicle driver is driving the motor vehicle and operating the shift lever and the accelerator pedal. At this time, if the no-load switch 19 is in the on-state (the shift lever takes the N or P position), as obvious from FIG. 9 the no-load potential EN at one end of the no-load switch 19 falls to the ground level through the starter 9 and the input voltage (no-load signal NL) at the CPU within the ECU 10 goes low in level. Accordingly, the decision of the CPU is that the automatic transmission 18 takes the out-of-gear state. On the other hand, if the no-load switch 19 is in the off-state, since the input potential (no-load signal NL) to the CPU goes high in level, the decision of the CPU is that it is in the in-gear state.
As a rule, in the engine control the fuel injection quantity varies in accordance with the in-gear state decision result, and hence the in-gear state decision is the information important for the engine system control and a high reliability is necessary. This also applies to the operation at start-up. However, the time of the in-gear state decision is not always coincident with the time at which a current actually flows into the starter 9. For example, as shown in a time chart of FIG. 10, when the speed Re of the engine 1 exceeds the set value Reo while the cranking starts and continues, then during that time the start decision means 24 decides, irrespective of the engine 1 being actually in a starting condition, that it is not in the starting condition and, hence, does not the start signal St. Moreover, if the circuit is arranged as shown in FIG. 9, the starter switch 11 comes into the on-state during the cranking even if the shift lever takes the N or P position (the no-load switch 19 is in the on-state), with the result that the input potential to the CPU comes into a high level and the ECU 10 makes a decision that the automatic transmission 18 is in the in-gear state (see FIG. 10). Accordingly, since the CPU decides in the in-gear state during the cranking regardless of whether or not the automatic transmission 18 actually takes the in-gear state (the shift lever actually takes the N or P position), there is a possibility that the start-up of the engine 1 and the exhaust gas deteriorate.
Therefore, the prior automatic transmission gear decision system suffers from a problem that, because as described above the start decision means 24 decides the start-up on the basis of the engine speed Re and the like but not using the starter switch 11 information, the time that the decision is made on the in-gear state is not always coincident with the time that a current actually flows into the starter 9 and, irrespective of actually the automatic transmission 18 being in the out-of-gear state, during the cranking the decision is made that the automatic transmission 18 is in the in-gear state, with the result that the start-up of the engine 1 and the exhaust gas deteriorate.